Total knee arthroplasty (TKA) has become one of the most widely used procedures for restoring knee function and relieving pain in the advanced stages of knee osteoarthritis; yet early TKA failure (<10 years post-surgery) remains a large-scale problem. Although knee instability is known to be a major cause of early failures, current methods for measuring knee balance are largely subjective and user-dependent. Ultrasound elastography (UE) is an innovative technology that enables the noninvasive quantification of soft tissue displacements and strains, which are important indicators of balance. We have recently developed such a technique for the evaluation of Achilles tendon deformation, and believe that this approach could provide important insight into knee soft tissue mechanics. The premise of this study is to use this noninvasive UE approach to measure knee balance in situ and then in patient populations to better understand the effects of TKA on altered knee balance, with the overall goal to pave the way toward intra-operative integration of this approach. In Aim 1, ultrasound data will be collected from cadaveric knee soft tissues (medial and lateral collateral ligament, patellar tendon) while functionally loaded in a kinematic knee rig. Tissue displacements and strains will then be computed using our UE approach. Results from UE will be compared with the current gold standard approach (digital image correlation; DIC) to enable calibration and then accuracy assessment. TKAs will then be performed on the specimens by an orthopedic surgeon, and altered knee balance will be imposed by overstuffing the medial or lateral components of the knee. The sensitivity of UE measurements to these altered balance conditions will be assessed. An important outcome of this aim will also be the public sharing of the validation dataset (ultrasound data, DIC and kinematics). In Aim 2, soft tissue mechanics will be evaluated in healthy adults (n=20), and adults with a prior TKA demonstrating acceptable (n=20) and unacceptable (n=20) stability. Comparison of UE- computed displacements and strains will provide insight into the effects of TKA on knee stability. Finally, in Aim 3, these results will be compiled and discriminant function analysis will be used to determine which tasks and measures provide the best discriminating power for clinical assessment. These data will be paired with clinical insight to provide recommendations for clinical integration of UE for the assessment of soft tissue knee balance. Successful completion of these aims will contribute to improving the outcomes of TKA for the more than 600,000 Americans who annually undergo this procedure, and will point to specific intra-operative techniques that can improve TKA outcomes.